Bob DBF
Contributor
For several years I did use a Fenzy. You see it in my Avatar. It was labeled "le parachute du plongeur".
It was NOT a BCD: no connection with the tank, no power inflator.
It had to be kept empty in normal conditions, and inflated with its small air tank just in case of an emergency.
Wearing a full Fenzy you float head up. No risk of drowning...
Of course I did modify it, installing a hose for filling it from the main tank and using it also as a BCD.
But I maintained the small tank and its safety function.
Before the BC, here in the US, we use a Mae West, which was a floatation device activated by a CO2 cartridge, or orally inflated, named after the life vest made famous in WWII. It was not a BC, but eventually adapted as one by some, and becoming the horse collar BC.
Mae West
Horse collar BC
The divers body is the center of mass and hangs below the horsecollar in the same manner a life jacket, which they were designed from.